--- title: "Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-655 - Solar Panel Comparison | ComparePV" description: "Compare Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-655 side by side: what actually differs, output when it is hot, thirty-year production, and the full specification." source: "https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-655" updated: 2026-09-11 --- # Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-655 655 leads on the differences that matter The largest is module efficiency: 0.50 pp more efficient. 16 of 19 comparable parameters are identical. ## The two panels | Attribute | A | B | | --- | --- | --- | | Panel | [Suntech STP-NT11/66QGDF-640](https://comparepv.com/panel/suntech-stp-nt11-66qgdf-640) | [Suntech STP-NT11/66QGDF-655](https://comparepv.com/panel/suntech-stp-nt11-66qgdf-655) | | Manufacturer | Suntech | Suntech | | Power | 640 Wp | 655 Wp | | Efficiency | 23.70 % | 24.20 % | | Technology | TOPCon | TOPCon | ## Where they differ Ranked by how much the difference matters, not by datasheet order. | Parameter | 640 | 655 | Difference | | --- | --- | --- | --- | | Module efficiency | 23.70 % | 24.20 % | +0.50 pp for 655 | | Power density | 236.9 Wp/m² | 242.5 Wp/m² | +5.6 Wp/m² for 655 | | Rated power | 640 Wp | 655 Wp | +15 W for 655 | ## Every compared parameter | Parameter | 640 | 655 | | --- | --- | --- | | Rated power | 640 Wp | 655 Wp | | Module efficiency | 23.70 % | 24.20 % | | Power density | 236.9 Wp/m² | 242.5 Wp/m² | | Open-circuit voltage | 49.70 V | 50.15 V | | Voltage at max power | 41.47 V | 41.91 V | | Short-circuit current | 16.22 A | 16.43 A | | Current at max power | 15.43 A | 15.63 A | | Temperature coefficient | -0.260 %/°C | -0.260 %/°C | | Dimensions | 2382x1134x30 mm | 2382x1134x30 mm | | Module area | 2.701 m² | 2.701 m² | | Weight | 33.1 kg | 33.1 kg | | Weight per kWp | 51.7 kg/kWp | 50.5 kg/kWp | | Product warranty | 15 yrs | 15 yrs | | Performance warranty | 30 yrs | 30 yrs | | Annual degradation | 0.35 %/yr | 0.35 %/yr | | Cell technology | TOPCon | TOPCon | | Cell type | Monocrystalline | Monocrystalline | | Cell count | 264 | 264 | | Bifacial | Yes | Yes | ## Thirty-year yield Each panel's own declared degradation curve, at 1,200 kWh/kWp a year Same temp coeff. for both panels (-0.260 %/°C), so a warmer roof scales both curves by the same factor: the totals fall together and neither panel gains on the other. - **Cumulative output, 640:** 21,640 kWh - **Cumulative output, 655:** 22,148 kWh - **Gap:** 508 kWh ## Output when hot | Condition | Cell temperature | 640 | 655 | Retained | | --- | --- | --- | --- | --- | | Standard test conditions | 25 °C | 640 W | 655 W | 100.0% of rated power | | Cool, bright day | 40 °C | 615 W | 629 W | 96.1% of rated power | | Typical summer roof | 55 °C | 590 W | 604 W | 92.2% of rated power | | Hot roof | 70 °C | 565 W | 578 W | 88.3% of rated power | ## Against the whole database | Measure | 640 | 655 | Out of | Note | | --- | --- | --- | --- | --- | | Efficiency | #517 | #184 | 14,005 | 655 leads by 333 places | | Power density | #521 | #172 | 14,005 | 655 leads by 349 places | | Heat behaviour | #511 | #511 | 14,005 | Tied - the same position in the database | | Weight | #5,083 | #3,911 | 14,005 | 655 leads by 1,172 places | | Warranty | #21 | #21 | 14,005 | Tied - the same position in the database | | Overall | #1,271 | #747 | 14,005 | 655 leads by 524 places | ## Questions ### Which panel is better: Suntech STP-NT11/66QGDF-640 or Suntech STP-NT11/66QGDF-655? According to our database: **Suntech STP-NT11/66QGDF-655** has higher module efficiency (**24.20%** vs **23.70%**). See the full spec comparison and 30-year energy simulation above for a complete picture. ### What is the efficiency of Suntech STP-NT11/66QGDF-640 and Suntech STP-NT11/66QGDF-655? **Suntech STP-NT11/66QGDF-640** has a module efficiency of **23.70%**, while **Suntech STP-NT11/66QGDF-655** is **24.20%**. Higher efficiency means more electricity from the same roof area - useful when space is limited. ### What cell technology does Suntech STP-NT11/66QGDF-640 use vs Suntech STP-NT11/66QGDF-655? **Suntech STP-NT11/66QGDF-640** uses **TOPCon** cells; **Suntech STP-NT11/66QGDF-655** uses **TOPCon**. Modern **n-type** technologies (**TOPCon**, **HJT**, BC) typically deliver higher efficiency and lower degradation compared to older **PERC** (p-type) cells. ### What is the warranty on Suntech STP-NT11/66QGDF-640 and Suntech STP-NT11/66QGDF-655? **Suntech STP-NT11/66QGDF-640** has a **30 years** power warranty; **Suntech STP-NT11/66QGDF-655** has a **30 years** power warranty. The power warranty guarantees a minimum percentage of rated output at the end of the warranty period (typically 80**-87%**). Product (materials) warranties are usually shorter. ### Are Suntech STP-NT11/66QGDF-640 and Suntech STP-NT11/66QGDF-655 bifacial panels? Both **Suntech STP-NT11/66QGDF-640** and **Suntech STP-NT11/66QGDF-655** are bifacial - they capture reflected light from the ground, which can add 5**-15%** more annual energy on ground-mount or elevated rooftop installations with a light surface beneath. ## Related comparisons - [Suntech STP-NT11/66QGDF-640 vs Suntech STP730S-D66-Nsh+](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp730s-d66-nsh) - 10 differences, the largest is rated power - [Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-670](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-670) - 4 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-665](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-665) - 3 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-660](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-660) - 3 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-650](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-650) - 3 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-640 vs Suntech STP-NT11/66QGDF-645](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-645) - One difference: module efficiency --- Source: https://comparepv.com/compare/suntech-stp-nt11-66qgdf-640/suntech-stp-nt11-66qgdf-655 Not in this file, on the page: the thirty-year yield curve year by year at a cell temperature you pick and a written summary generated on request.